Adhesive



Patented Aug. 23,1938

- UNITED STATES ADHESIVE I Franklin S. Smith, New Haven, Conn.

No Drawing. Application April 27,1934,

- Serial No. 722,685

4 Claims.

This invention relates to adhesives and more particularly to thermoplastic adhesives for sealing-and labeling packaged products that are, after packaging, electrically treated.

I One of the objects of this invention is to provide a suitable and satisfactory adhesive for sealing and labeling the packages of products, such as cereals and like food products that are, after packaging and sealing and/or labeling, subject- 'ed to electrical sterilization. Another object is to provide an adhesive of the above-mentioned nature that will satisfactorily meet the reduirements of machine packaging and that will not detrimentally affect the subsequent electrical I sterilization of the packaged products, Another object isto. provide an adhesive of the abovementioned character that will have a suitable dielectric strength of an order adequate to prevent interference with satisfactory electrical 9 sterilization of the contents of the package on which the adhesive is employed. Another object is to provide an adhesive of the above-mentioned character that will be inexpensive, thoroughly dependable in action, and well adapted to meet the numerous peculiar practical requirements. Other objects will be in part obvious or in part pointed out hereinafter.

The invention accordingly consists in the features of construction, combinations of elements, D and arrangements of parts as will be exemplifled in the processes and products to be hereinafter described and the scope of the application of which will be indicated in the following claims. a 5 As conducive to a clearer understanding of certain' features of'this invention, reference might first be made to my co-pending application Se- 3 rial No. 558,069, filed August 19, 1931, entitled Art and apparatus for sterilizing, now Patent 1. No. 1,959,390, issued May 22, I934, inwhich I have disclosed a method and apparatus for electrically sterilizing food and other products, particularly packaged products, in accordance with which the food or like products, containing ini sects, and/or their eggs, larvae, or pupae, is subvjected to a local high voltage disruptive discharge, illustratively taking the form of a local corona discharge as explained in detail in the above-mentioned application, whereby the insect l life is destroyed.

Various unique actions and electric and dielectric phenomena that take place, particularly where the material is packaged in packages of pasteboard, paper, boxboard, or the like, are i sufll'ciently set forth-and described in my aforesaid application, to which reference for such-purposes may be made. It may here, however, be noted that the packaged material, for example, corn meal, flour, or the like, and assumed to'be contaminated with insect life, may be consid 5 ered as a heterogeneous dielectric made up of various dielectrics in series multiple arrangement and containing isolated capacities, the latter being the contaminations represented by the various stages of insect life. If the material is packaged, the pasteboard, paper, or the like, of the package itself constitutes a dielectric of one permittivity, the individual particles of the meal, flour, or the like, constituting a dielectric of still another permittivity, and the air intervening these particles constitutes still another dielectric but one of lowest permittivity of all, namely, unity. When this heterogeneous dielectric enters the treatment zone underneath the high voltage electrodes, the dielectrics of higher permittivity cause overstressing of the air dielectric with resultant ionization and break-down thereof; but the contaminating particles, such as insects, eggs, larvae or pupae thereof, are of substantially infinite permittivity and are in effect conducting so that the corona streamers, re-

sulting from the above-mentioned ionization and break-down of the air dielectric, virtually seek out and pass through these contaminating particles and thus eifectivelybring about their destruction. Other coactions and particularly those whereby puncturing of the material of the carton or package is prevented also take place,

as set forth in my aforesaid application.

The packages of-the product to be sterilized as by the above-described or referred-to apparatus and process preferably are moved, as by a suitable conveyer-belt into and then out of the treatment zone, a single passage through the treatment zone being adequate, and in certain practical installations or uses of the above-described apparatus or process it is desirable and expedient to aline the packaging machine andthe sterilizing apparatus so that the packaged product discharged from the packaging machine is immediately received by the sterilizing apparatus and passed through the latter at a rate commensurate with the rate of discharge of packages from the packaging machine. It is particularly under such circumstances that the adhesive employed in the packaging machine for sealing the package or its flaps or closure members or labels, or what-not, meets certain re-= quirements or desiderata laid down by the action that takes place in the treatment zone of 66 brought about by the materials of, different permittivities as above briefly set forth, let 'itbe assumed that the adhesive employed 'on' 'the packages reaches the treatment zone with a sufficient moisture content so that the adhesive has a relatively high permittivity, say, on the order of the permittivity of the contaminating particles of insect life, and let it be assumed that the adhesive is employed to stick down the flaps or sides of the'package whose plane extends in the direction of the dielectric field in the treatment zone; in such case, the high permittivity of the adhesive would result in an action analogous to the action brought about by the high permittivity of the particles of insect life in that the corona or disruptive discharge would seek out, as a path of travel, the adhesive itself, thus in effect shortcircuiting, as it were, the discharge through the adhesive and shunting it away from at least portions of the product within the package, such portions thus escaping treatment or sterilization.

Bearing in mind, also, how the material of the package itself coacts with other features of construction and action as described in my abovementioned application-whereby puncturing of the material of the package is prevented and assuming that the adhesive is applied to that side or wall of the carton or package whose plane extends at substantially right angles to the direction of the high voltage dielectric field, the high permittivity of the adhesive (still assuming an adhesive of, for example, a high moisture content) might cause such redistribution of potential drops (inversely as the permittivities of the dielectrics that are serially alined) as might actually effect puncturing of the material of the carton itself.

One of the dominant aims of this invention is, therefore, to provide adhesives and sealed cartons or packages having physical and electrical properties enabling their use in electrical sterilizing apparatus or in a process such as those above-mentioned and to provide adhesives capable of meeting the various desirable characteristics for use in packages for food products or for use in automatic packaging machines while having adequate. electrical properties to avoid detrimental interference with the electrical sterilizing action of the subsequently employed apparatus or process.

Where, as in the preferred embodiment of my invention, the adhesive is to be automatically applied to the package or carton, or label or parts thereof, for closing or sealing the flaps or closures of the carton or package or to apply, the label thereto, as by any suitable packaging or sealing or label-applying machine, it is desirable that the adhesive have certain qualities or characteristics. Among the latter may be noted the following:- For certain types of machines, such as the reciprocating type, the adhesive should be non-stringing though that quality is of less importance in other types of machines, such as in so-called straight line gluing as in certain types of carton-forming machines. It is desirable to have it non-foaming, especially when used in high speed machines. It should be chemically neutral to .the materials or parts of the machine contacted by the adhesive. It should have suitable initial tack; if it has appropriate initial tack the quality of quick setting becomes less important because, if the initial tack is sufficient to hold the parts to the electrical sterilizing apparatus. For examv ,-be secured together during the relatively short ple, and bearing in mind the actionsthat are time of the machine-packaging operation, the

f time interval for ultimate setting becomes rela- ,It' is advantageous if the adhesive is'soluble in water as thereby the cost of cleaning the machine-ry is less than if other solvents, such as organic solvents, have to be employed, while also there is thereby avoided the fire hazard of many of the less expensive organic solvents available. Also, the adhesive should have appropriate viscosity, this factor being material particularly where the adhesive is applied by automatic machines and preferably the adhesive should be capable of having its viscosity varied throughout an appropriate range inasmuch as the viscosity requirements vary somewhat with the type of machine employed, the purpose of use, and other conditions met with in practice. Preferably, also, the vapor pressure should be low at the temperature of application and the vapors should not be obnoxious.

Where the adhesive is employed for use in or on packages, and especially on packages that contain or are to contain food products, the adhesive desirable has certain other characteristics or properties. For example, where food products are involved, the adhesive should be non-toxic and it should be odorless, particularly where the food or other products are susceptible to odor absorption. It is desirable also that the adhesive be of about the same color as the material of the package. It is desirable that the adhesive be 1 chemically neutral with respect to the materials Where employed in connection with packages,

cartons, containers, or the like, which, with their contents, are to be subjected to electrical sterilizar' tion as by the apparatus or process above referred to and more fully set forthin my above-mentioned co-pending application, the dielectric properties of the adhesive are important, as has already been above, indicated, and certain of the desirable properties and characteristics of the adhesive in this respect are dealt with in moredetail hereinafter. The carton, package, container, or the like, employing or having embodied therein an adhesive meeting particularly these dielectric requirements has, furthermore, the distinctive advantage and uniqueness of action in that it or they may be confidently subjected, with their contents, to the electric discharge and particularly to the high voltage dielectric field without fear of puncturing the carton or package itself,'witliout disturbing uniformity of sterilization of the contents and achieve these advantagesand results irrespective of whether or not the adhesive has already set or hardened. To meet these requirementsin a package employing adhesive and in the adhesive itself, I first provide a thermoplastic adhesive as follows:

Illustratively and preferably I employacetamide and dextrin; these constituents are combined by fusing them together at a suitable temperature illustratively a temperature of preferably within the range from 80 C. to 120 0., working the mixture by any suitable mechanical .or other means, until the dextrin has been dissolved or combined. In fusing these two materials together the acetamide is heated to a temperature at or above 80 degrees C., at which temperature it becomes. 'a liquid. To this liquid acetamide the desired quantity of the other ingredient, such as acetamide and on the order of 55% by weight of dextrin. After the mixing has been achieved. the comingled or combined constituents are allowed to cool; for example, it maybe poured into shallow pansto achieve quicker cooling. During this cooling process the composition in effect crystallizes. It may then, if desired,-be broken up or crushed into particles of desired size and I preferably break it up for greater ease in handling and packaging and shipment. In this condition the adhesive is not sticky to the touch and the pieces ,or particles thereof do not adhere to:0ne another;

it can, therefore, be shipped in suitable containers which preferably are moisture resisting.

In using the adhesive, a suitable quantity of the material is placed in a suitable container and is heated in any suitable manner, thus to convert it from the solid or solidified form to the liquid or plastic form suitable for application. The temperature of application of the adhesive, as in anysuitable automatic packaging or sealing or label-applying machine, is not critical and may be varied, depending upon various conditions, such as degree of viscosity desired, or the like, and the temperature of application may be illustratively within the range from about 80 C. to about 140 C. By similarly combining under substantially similar conditions as just set forth and in approximately similar proportions, acetamide with oneor'more other ingredients, which may be proteins, carbohydrates, or resins, such as starches, dextrins, dextrin gums, c'aseins, lignins, or shellac, or with combinations of the latter, I am enabled to achieve an adhesive having the characteristics and properties above set forth.

In substantially like manner and with commensurately similar results, I may combine with acetamide both hydrophilic and organophilic colloids; the resultant adhesive is particularly adaptable for joining two otherwise incompatible solids.

The ingredient acetamide is crystalline; it does not of itself possess adhesiveness or deformability. It has a relatively high heat of fusion. The secondary ingredient, being one or more of substances like those above-mentioned in detail is,

' in general, amorphous and contributes to the resultant adhesive a number of important properties such as initial tack, adhesiveness, deform-w; ability, and others. The primary or first-mentioned ingredient (acetamide) because of its high heatof fusion is instrumental in giving the resultant adhesive the desirable high thermal capacity. To this thermal capacity the secondary ingredient contributes somewhat at least to the extent of its own specific heat.

As above pointed out, a relatively wide range Q of substances may be combined with the acetamide. Acetamide (CHaCONHz) has several groups of molecules; for example, it has a tautomeric hydroxyl group, giving it a solvent action analogous to that of water and alcohol. It includes a methyl group, giving it a solvent action analogous to that of hydrocarbons. It has a carbonyl group, giving it a solvent action analosons to that, for example, of ketones. It has an am de group, giving it a solvent action analogous to the ammonia derivatives. In this manner it may coact, toachieve the adhesive of my invention, to numerous classes of. substances or ingredients, as earlier above described. Thus, also, I

may combine it with amorphous colloids that are found to have numerous desirable and important properties, some of which are mentioned hereinafter; for example, so far as I am aware, it is the only adhesive which, particularly when used under the" conditions met within packaged goods, will stand both cold and heat throughout satisfactory ranges. For instance, the parts secured together by this adhesive, such as the flaps or parts of a boxboard box will not separate or snap apart even though the temperature is as low as 40 C. or as high as 40 0. Moreover. even under temperatures on the order to 40 C. and in an atmosphere 100% humid, the securing action of the adhesive remains unimpaired.

As pointed out more fully hereinafter, the d electric properties of my adhesive meet in par ticular the above-described requirements of noninterference with the di-electric field in the electric sterilizing process or machine substantially parts, to a condition of non-conductivity, is so rapid that interference with the electrical ac-. tions in sterilizing the contents of the package or container does not take place. Particular] where the adhesive is applied in a very thin fling:

such as a film of several .thousandths of an inch in thickness, the transition to the non-conductive phase takes place at relatively great rapidity.

The adhesive, made according to the above, satisfactorily meets the requirements and has the desirable properties or characteristics above set forth. For example, the high thermal capacity of the adhesive coacts in a unique and highly advantageous manner. In most automatic sealing 'or packaging machines, the adhesive is applied to, only one of the two surfaces of the package or carton or shell, or the like, to be sealed or secured together. By reason of the high thermalcapacity of 'my adhesive, sufllcient heat is available to be transferred or dissipated to the uncoated part or surface, when the-two surfaces between), to cause the adhesive to adhere dependably thereto. In some types of apparatus the delay between the time of application of the adhesive to the surface of a flap or part and the time that this surface is pressed into engagement with the surface of the coacting flap or part is relatively substantial; yet the high thermal capacity of my adhesive insures the maintenance of an carton or container as have to depend upon an adhesive are secured -'together or held in place by an adhesive made according to one of the numerous prescriptions above defined. Where the carton, shell, package, or the like, is made of a suitable paper, or cardboard, or so-called boxboard, or like or equivalent materials, and has this adhesive embodied therein, the electrical actions that take place are important. For example, the dielectric strength of the adhesive is substantially the same as'that of the cardboard,

paper, boxboard, or other material that is used as the packaging material. lVIore particularly, the earlier above-mentioned transition from a conducting phase or condition to a non-conductive or insulating phase is so rapid, particularly under the conditions of application of the adhesive in completing .the packaging or cartoning of the material to be sterilized, that the completed or sealed packages may be discharged from the packaging machine directly into the treatment zone. This transition period may be on the order of fifteen seconds in length and the transition takes place even though the adhesive is not set. The setting may require vastly more time and may take place after the electrical treatment. Apparently the non-conductive phase is brought about immediately upon the commencement of crystallization-of the adhesive, once the latter is applied to the part or parts to be secured together.

When, therefore, the package enters the treatment zone and is subjected to the high voltage dielectric field, no detrimental redistribution of dielectric stresses as between the adhesive and the packaging material takes place and thus rupture or puncture and other detrimentalelectrical actions are precluded from taking place. Moreover, the dielectric properties of the adhesive in the resultant combination of dielectric and packaging material, in the package construction, are such that, whether the adhesive extends in a plane or direction transversely of the dielectric field (as it would if embodied in the top or bottom of the package) jor extends in the general direction of the dielectric field it- 2,127,540 are brought together (with the adhesive thereself (as it does when embodied in the sides or ends of the package), uniform distribution of the corona or. electric discharge is not interfered with and thus all portions of, the contents of.

package embodying the adhesive may be subjected to the' above-mentioned electrical treatment immediately upon discharge thereof from the automatic packaging or sealingmachine, thus achieving important practical advantages, some of which have been indicated earlier hereinabove.

-- Thus, it will be seen that there has been provided in this invention an adhesive and a package embodying the combination of a dielectric 'packaging material and adhesive in which the various objects hereinbefore noted together with many thoroughly practical advantages are successfully achieved.

As many-possible embodiments may be made of the above invention and as many changes might be made in the embodiment above set forth, it is to be understood that all matter hereinbefore set forth is to be interpreted as illustrative and not in a limiting sense.-

1. A thermoplastic adhesive of the type having an appreciable initial tack, a predetermined temperature of solidification, and an appreciable heat of fusion, in combination, acetamide and an armorphous colloid in an amount to impart adhesiveness and deformability.

2. A thermoplastic adhesive of the type having an appreciable initial tack and a predeter mined temperature of solidification, in combination, acetamide'anda hydrophilic adhesive colloid in an amount to impart adhesiveness and deformability.

3. A thermoplastic adhesive cf the type 'having an appreciable initial tack and a predetermined temperature of solidification, in combina tion, acetamide and an organophilic adhesive colloid in an amount to impart adhesiveness and deformability.

4. A thermoplastic adhesive -of the type having an appreciable initial tack and a predeterminedtemperature of solidification, comprising, in combination, acetamide and an adhesive material in an amount to impart adhesiveness and deformability, said adhesive material being of the class of hydrophilic and organophilic materials.

FRANKLIN S. SMITH. 

